Spring lock outside for unlawful entry (8)
I believe the answer is:
trespass
'unlawful entry' is the definition.
(thesaurus)
'spring lock outside' is the wordplay.
'spring' becomes 'spa' (I've seen this before).
'lock' becomes 'tress' (I've seen this before).
'outside' indicates putting letters inside.
'spa' placed within 'tress' is 'TRESPASS'.
'for' is the link.
(Other definitions for trespass that I've seen before include "Enter land without permission" , "Intrude on another's property" , "Go where one shouldn't" , "Enter another's property unlawfully" , "Wrong" .)